The present invention relates to a liquid crystal display(LCD), more particularly to a homogeneous electric field LCD capable of preventing generating parasitic electric field.
The in-plane switching(IPS) mode LCD of the homogeneous electric field has been suggested to replace the twisted nematic (TN) mode LCD so that the viewing angle characteristic is improved.(Principle and characteristic of electro-optical behaviour with in-plane switching mode, Asia Display 95, p. 577xcx9c580)
FIG. 1 is a cross-sectional view showing a conventional IPS mode LCD.
A counter electrode 12 is disposed on a lower substrate 11. An insulating layer 13 is disposed on the lower substrate in which the counter electrode 12 is formed. A pixel electrode 14 is sandwiched between the counter electrodes 12 on the insulating layer 13. A passivation layer 15 and a first alignment layer 16 are formed in series on the lower substrate in which the pixel electrode 14 and the counter electrode 12 are formed.
An upper substrate 17 is opposed to the lower substrate with a selected distance. A second alignment layer 18 is formed on an inner surface of the upper substrate 17. A liquid crystal layer 19 is sandwiched between the upper substrate 17 and the lower substrate 11.
However, there are generated residual DC components and static electricity in the IPS mode LCD. Therefore afterimages are shown in the LCD.
That is to say, driving electric power of the LCD is AC components and driving velocity is about several tens xcexcs. On the other hand, liquid crystal molecule of the LCD device have reaction velocity of several ms. Accordingly, when the LCD is driven by providing the AC power, the liquid crystal molecules in the liquid crystal layer 19 do not react to the frequency of the driving electric power but change their polarities. Therefore, a DC due to a DC power is generated between the counter electrode 12 and the pixel electrode 14. To remove the DC, voltage of the counter electrode 12 is offset. However, this offsetting of the counter electrode voltage can not remove the DC components between the counter and pixel electrodes completely. Also, the residual DC components are accumulated in proportion to time.
After a lapse of time, particles having negative electric charge among contaminants in the liquid crystal layer 19 gather around the residual DC component having positive electric charge. As a result, there is generated a parasitic electric field between the residual DC component and the contaminants of the liquid crystal layer 19. The parasitic electric field offsets by a main electric field being formed between the counter electrode 12 and the pixel electrode 14, and then the liquid crystal molecules drive in an abnormal state. Furthermore, the voltage holding ratio in the liquid crystal layer 19 is degraded and causes afterimages on the screen. Also, the residual DC components reduce effective voltage of the LCD thereby deteriorating response time characteristic of the LCD.
Moreover, there is attached to a surface of an analyzer a protection film for protecting screen of finished product. This protection film should be peeled off when a consumer uses the LCD device. At this time, there is generated static electricity by charging between the protection film and the analyzer momentarily.
As described, the static electricity is generally discharged by electrodes provided within the LCD cells. However, there is no electrode at an upper substrate of the IPS mode LCD, and accordingly it is not easy to discharge the static electricity and the static electricity remains in the upper substrate.
In that case, a parasitic electric field is formed between the residual static electricity in the upper substrate and electrodes of a lower substrate, thereby deteriorating the display characteristic of the LCD.
Accordingly, it is one object of the present invention to prevent generating of parasitic electric field due to the residual DC.
It is further object of the present invention to prevent generating parasitic electric field due to the residual static electricity in the upper substrate.
It is still object of the present invention to improve response time of the LCD.
To accomplish foregoing objects, the present invention provides an LCD comprising: a substrate; counter electrodes formed on the substrate; pixel electrodes formed on the substrate and spaced apart from the counter electrodes; and a high dielectric layer disposed between the counter and pixel electrodes on the substrate in which the counter and pixel electrodes are formed.
Herein, both sides of the high dielectric layer are overlapped with the counter electrodes and the pixel electrodes respectively, otherwise the high dielectric layer is overlapped with the counter electrodes and the pixel electrodes entirely.
The present invention further provides an LCD comprising: a first substrate; counter electrodes formed on the first substrate; pixel electrodes formed on the first substrate and spaced apart from the counter electrodes; a second substrate opposed to the first substrate; and a high dielectric layer disposed at an inner face of the second substrate.
Herein, the high dielectric layer is disposed over the second substrate, or the high dielectric layer is formed at a region to correspond with a region between the counter and pixel electrodes, otherwise the high dielectric layer is formed at a region to correspond with the counter and pixel electrodes.
The present invention still provides an LCD comprising: a first substrate; counter electrodes formed on the first substrate; pixel electrodes formed on the first substrate and spaced apart from the counter electrodes; a first high dielectric layer formed between the counter and pixel electrodes on the first substrate in which the counter and pixel electrodes are formed; a second substrate opposed to the first substrate; and a second high dielectric layer disposed at an inner surface of the second substrate.
Herein, the high dielectric layers have a dielectric constant of over 8, and more preferably the high dielectric layers have a dielectric constant of 106 approximately.
According to the present invention, the high dielectric layer having dielectric constant of over 8 is sandwiched between the substrate in which the counter and pixel electrodes are formed and the alignment layer, thereby reducing the residual DC between the counter and pixel electrodes. As a result, no parasitic electric field is formed in the liquid crystal layer and the voltage holding ratio and response time characteristic are also improved. Further, since the parasitic electric field is prevented, the liquid crystal molecules do not drive in the abnormal state. Consequently, wide viewing angle and enhance transmittance are obtainable.
Further, the static electricity in the upper substrate is discharged rapidly since the high dielectric layer is formed on the upper substrate opposite to the lower substrate in which the counter and pixel electrodes are formed.